Proper perishable food management requires those involved in transporting, storing or preparing food to appropriately monitor and keep records of conditions in which food is kept. Food safety regulations, such as HACCP and FDA Food Safety Modernization Act (FSMA), require the implementation of certain procedures and monitoring protocols for managing perishable food safety and quality. Perishable goods include but are not limited to perishable foods such as fresh or frozen meats, vegetables, fruits, breads, milk and milk products such as cheese and the like.
Such perishable food is often transported and stored in environments where certain conditions need to be controlled. For example, perishable food items may need to be refrigerated or frozen in order to maintain freshness. If food is not stored in an environment under the proper conditions, the food may spoil immediately or before its expected expiry date. It is important for the owners of perishable goods to be able to track the conditions in the environments where those goods are stored. It is also important for purchasers of perishable goods to know that such purchased goods have been kept in the proper conditions.
For example, it is common for perishable foods to be transported in refrigerated vehicles. The foods may be shipped from a warehouse and transported in a refrigerated trailer. In many cases, there is no oversight provided to ensure that the food was kept at the proper temperature for the duration of the trip. In many cases, a driver will sign a form at the conclusion of the trip that in an effort to verify the food was maintained in proper conditions. It may be impossible to independently confirm whether the driver left the trailer door open or whether the refrigeration unit temporarily failed at some point during the journey.
Another situation where it is important to track environmental conditions is in freezers and refrigerators in restaurants and grocery stores. Restaurants often have walk-in freezer and/or refrigeration units that require temperature regulation. Grocery stores will have multiple freezer and refrigeration units for displaying food for sale. It is very important to keep the temperatures of these freezer or refrigerator units at a certain level to ensure that the food does not spoil. The temperature within a freezer unit may need to be checked and logged frequently, in some cases more than once a day. In some cases, a person may need to physically enter the freezer or refrigerator to check the temperature in the unit and then enter the measured temperature into a log. Physically entering the freezer unit is undesirable because it causes loss of heat from the freezer and may increase the risk that the door is accidentally left open, thereby causing the food to spoil. It may be difficult to track temperatures in freezer units at restaurants because it is common for regulations to require that any items that are placed inside a restaurant refrigerator or freezer must be made from a food-grade material requiring special thermometers.
Furthermore, freezers will often have a defrost cycle, during which the temperature within the unit may increase. The operation of the defrost cycle may prevent the use of a simple temperature switch. A temperature switch would cause an alarm condition when the temperature in the freezer rose above a set level. However, the temperature switch would identify false alarms during a defrost cycle. On the other hand, a sensor that is programmed to ignore a defrost cycle may also be ineffective, because a freezer unit can fail after the defrost cycle is completed, at which point the unit fails to turn back.
Another issue that exists in dealing with technology for sensing conditions in environments with low temperatures is that often batteries are less effective in cold conditions. For example, although lithium batteries may operate to below minus 40 degrees Celsius, the battery capacity may be reduced by more than half at those temperatures. For portable temperature sensors to be effective, it is important to have a long battery life. On the other hand, high powered batteries may be undesirably heavy and bulky. Furthermore, active radio transmitters on portable sensors require an energy source, unlike traditional passive RFID tags. Many portable sensors with active radio transmitters may have prohibitively short battery lives when used in applications where the sensors are exposed to in cold conditions.
Some portable sensor systems induce a sleep function during which the sensor is dormant. For example, U.S. Pat. No. 7,495,558 to Pope et al. (“Pope”) describes an RF label that may be applied to a packaged product to track its shelf life. In some embodiments, the system has a power management module that periodically wakes up a freshness monitoring component from a sleep or other low power state to gather the sensor measurements. The system is connected to an individual packaged item and tracks freshness at set intervals.
The system in Pope tracks freshness at set timed intervals. However, product freshness may be heavily impacted during a change of state of the environment surrounding the product, such as when the product is moved between two separate environments or where a refrigerator is opened. For example, if a product is unloaded from a transportation trailer and placed outside on a hot day before ultimately being loaded into a restaurant freezer, a timed sensor may not take a reading during the short time in which the product is left outside. However, the packaged product may spoil quite rapidly in hot conditions, which may not be detected by the system in Pope.
Furthermore, the Pope system is described as being placed on the outside packaging for items such as wine or pharmaceuticals, where sterilization and food safety are not a concern. Food distribution and retailing is typically a high volume and low margin activity. As such new technologies, which typically are expensive, are not readily adapted into the food industry due to cost concerns. Thus, any solutions in the food industry have to be very cost effective. Individual sensors for each package of product can be very expensive, and may make the technology uneconomic.
Other patents and patent applications of general interest in the field of portable sensors include:                U.S. Pat. Nos. 5,313,848, 6,285,282, 7,151,455, 7,495,558, 7,538,672, 7,592,916, 7,784,707, 7,808,383, 7,828,345, 7,866,555, 7,937,244, 8,047,432, 8,223,680, RE 40,073; and        U.S. Patent Application Publication Nos. 2003/0163287, 2004/0100379 2007/0171076, 2011/0029413, 2012/0111044, 2012/0252488.        
Therefore there is a continuing need for a sensing device that is portable, has a long battery life, is suitable for contacting food items and allows for efficient tracking of important events during the operation of the device. Further such a device needs to be cost effective and useful in respect of a wide variety of perishable items.